CGDCONFIG(8) NetBSD System Manager's Manual CGDCONFIG(8)
NAMEcgdconfig -- configuration utility for the cryptographic disk driver
SYNOPSIScgdconfig [-npv] [-Vvmeth] cgd dev [paramsfile]
cgdconfig -C [-nv] [-fconfigfile]
cgdconfig -U [-nv] [-fconfigfile]
cgdconfig -G [-nv] [-iivmeth] [-kkgmeth] [-ooutfile] paramsfilecgdconfig -g [-nv] [-iivmeth] [-kkgmeth] [-ooutfile] alg [keylen]
cgdconfig -s [-nv] [-iivmeth] cgd dev alg [keylen]
cgdconfig -u [-nv] cgdDESCRIPTIONcgdconfig is used to configure and unconfigure cryptographic disk devices
(cgds) and to maintain the configuration files that are associated with
them. For more information about cryptographic disk devices see cgd(4).
The options are as follows:
-C Configure all the devices listed in the cgd configuration
file.
-fconfigfile Specify the configuration file explicitly, rather than
using the default configuration file /etc/cgd/cgd.conf.
-G Generate a new paramsfile (to stdout) using the values
from paramsfile which will generate the same key. This
may need to prompt for multiple passphrases.
-g Generate a paramsfile (to stdout).
-iivmeth Specify the IV method (default: encblkno1).
-kkgmeth Specify the key generation method (default:
pkcs5_pbkdf2/sha1).
-n Do not actually configure or unconfigure a cryptographic
disk device, but instead report the steps that would be
taken.
-ooutfile When generating a paramsfile, store it in outfile.
-p Read all passphrases from stdin rather than /dev/tty.
Passphrases are separated by newlines. Users of this
flag must be able to predict the order in which
passphrases are prompted. If this flag is specified then
verification errors will cause the device in question to
be unconfigured rather than prompting for the passphrase
again.
-s Read the key from stdin.
-U Unconfigure all the devices listed in the cgd configura-
tion file.
-u Unconfigure a cgd.
-Vvmeth Specify the verification method (default: none).
-v Be verbose. May be specified multiple times.
For more information about the cryptographic algorithms and IV methods
supported, please refer to cgd(4).
Key Generation Methods
To generate the key which it will use, cgdconfig evaluates all of the key
generation methods in the parameters file and uses the exclusive-or of
the outputs of all the methods. The methods and descriptions are as fol-
lows:
pkcs5_pbkdf2/sha1 This method requires a passphrase which is entered at
configuration time. It is a salted hmac-based scheme
detailed in ``PKCS#5 v2.0: Password-Based Cryptography
Standard'', RSA Laboratories, March 25, 1999, pages
8-10. PKCS #5 was also republished as RFC 2898.
pkcs5_pbkdf2 This is an earlier, slightly incorrect and deprecated
implementation of the above algorithm. It is retained
for backwards compatibility with existing parameters
files, and will be removed. Existing parameters files
should be converted to use the correct method using
the -G option, and a new passphrase.
storedkey This method stores its key in the parameters file.
randomkey The method simply reads /dev/random and uses the
resulting bits as the key. It does not require a
passphrase to be entered. This method is typically
used to present disk devices that do not need to sur-
vive a reboot, such as the swap partition. It is also
handy to facilitate overwriting the contents of a disk
volume with meaningless data prior to use.
urandomkey The method simply reads /dev/urandom and uses the
resulting bits as the key. This is similar to the
randomkey method, but it guarantees that cgdconfig
will not stall waiting for hard-random bits (useful
when configuring a cgd for swap at boot time). Note,
however, that some or all of the bits used to generate
the key may be obtained from a pseudo-random number
generator, which may not be as secure as the entropy
based hard-random number generator.
shell_cmd This method executes a shell command via popen(3) and
reads the key from stdout.
Verification Method
The verification method is how cgdconfig determines if the generated key
is correct. If the newly configured disk fails to verify, then cgdconfig
will regenerate the key and re-configure the device. It only makes sense
to specify a verification method if at least one of the key generation
methods is error prone, e.g., uses a user-entered passphrase. The fol-
lowing verification methods are supported:
none perform no verification.
disklabel scan for a valid disklabel.
ffs scan for a valid FFS file system.
re-enter prompt for passphrase twice, and ensure entered passphrases
are identical. This method only works with the
pkcs5_pbkdf2/sha1 and pkcs5_pbkdf2 key generators.
/etc/cgd/cgd.conf
The file /etc/cgd/cgd.conf is used to configure cgdconfig if either of -C
or -U are specified. Each line of the file is composed of either two or
three tokens: cgd, target, and optional paramsfile.
A `#' character is interpreted as a comment and indicates that the rest
of the line should be ignored. A `\' at the end of a line indicates that
the next line is a continuation of the current line.
See EXAMPLES for an example of /etc/cgd/cgd.conf.
Parameters File
The Parameters File contains the required information to generate the key
and configure a device. These files are typically generated by the -g
flag and not edited by hand. When a device is configured the default
parameters file is constructed by taking the basename of the target disk
and prepending /etc/cgd/ to it. E.g., if the target is /dev/sd0h, then
the default parameters file will be /etc/cgd/sd0h.
It is possible to have more than one parameters file for a given disk
which use different key generation methods but will generate the same
key. To create a parameters file that is equivalent to an existing
parameters file, use cgdconfig with the -G flag. See EXAMPLES for an
example of this usage.
The parameters file contains a list of statements each terminated with a
semi-colon. Some statements can contain statement-blocks which are
either a single unadorned statement, or a brace-enclosed list of semi-
colon terminated statements. Three types of data are understood:
integer a 32 bit signed integer.
string a string.
base64 a length-encoded base64 string.
The following statements are defined:
algorithm string
Defines the cryptographic algorithm.
iv-method string
Defines the IV generation method.
keylength integer
Defines the length of the key.
verify_method string
Defines the verification method.
keygen string statement_block
Defines a key generation method. The statement_block contains
statements that are specific to the key generation method.
The keygen statement's statement block may contain the following state-
ments:
key string
The key. Only used for the storedkey key generation method.
cmd string
The command to execute. Only used for the shell_cmd key gener-
ation method.
iterations integer
The number of iterations. Only used for pkcs5_pbkdf2/sha1 and
pkcs5_pbkdf2.
salt base64
The salt. Only used for pkcs5_pbkdf2/sha1 and pkcs5_pbkdf2.
FILES
/etc/cgd/ configuration directory, used to store params-
files.
/etc/cgd/cgd.conf cgd configuration file.
EXAMPLES
To set up and configure a cgd that uses AES with a 192 bit key in CBC
mode with the IV Method `encblkno1' (encrypted block number):
# cgdconfig -g -o /etc/cgd/wd0e aes-cbc 192
# cgdconfig cgd0 /dev/wd0e
/dev/wd0e's passphrase:
When using verification methods, the first time that we configure the
disk the verification method will fail. We overcome this by supplying -Vre-enter when we configure the first time to set up the disk. Here is
the sequence of commands that is recommended:
# cgdconfig -g -o /etc/cgd/wd0e -V disklabel aes-cbc
# cgdconfig -V re-enter cgd0 /dev/wd0e
/dev/wd0e's passphrase:
re-enter device's passphrase:
# disklabel -e -I cgd0
# cgdconfig -u cgd0
# cgdconfig cgd0 /dev/wd0e
/dev/wd0e's passphrase:
To create a new parameters file that will generate the same key as an old
parameters file:
# cgdconfig -G -o newparamsfile oldparamsfile
old file's passphrase:
new file's passphrase:
To configure a cgd that uses Blowfish with a 200 bit key that it reads
from stdin:
# cgdconfig -s cgd0 /dev/sd0h blowfish-cbc 200
An example parameters file which uses PKCS#5 PBKDF2:
algorithm aes-cbc;
iv-method encblkno1;
keylength 128;
verify_method none;
keygen pkcs5_pbkdf2/sha1 {
iterations 39361;
salt AAAAgMoHiYonye6Kog \
dYJAobCHE=;
};
An example parameters file which stores its key locally:
algorithm aes-cbc;
iv-method encblkno1;
keylength 256;
verify_method none;
keygen storedkey key AAABAK3QO6d7xzLfrXTdsgg4 \
ly2TdxkFqOkYYcbyUKu/f60L;
An example /etc/cgd/cgd.conf:
#
# /etc/cgd/cgd.conf
# Configuration file for cryptographic disk devices
#
# cgd target [paramsfile]
cgd0 /dev/wd0e
cgd1 /dev/sd0h /usr/local/etc/cgd/sd0h
Note that this will store the parameters file as /etc/cgd/wd0e. And use
the entered passphrase to generate the key.
DIAGNOSTICScgdconfig: could not calibrate pkcs5_pbkdf2 An error greater than 5% in
calibration occured. This could be the result of dynamic processor fre-
quency scaling technology. Ensure that the processor clock frequency
remains static throughout the program's execution.
SEE ALSOcgd(4)
``PKCS #5 v2.0: Password-Based Cryptography Standard'', RSA Laboratories,
March 25, 1999.
HISTORY
The cgdconfig utility appeared in NetBSD 2.0.
BUGS
Since cgdconfig uses getpass(3) to read in the passphrase, it is limited
to 128 characters.
NetBSD 6.0 October 19, 2009 NetBSD 6.0

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